Conventional approaches for detecting scene changes analyze the recorded bitstream. Such analysis may use the results of a discrete cosine transform (DCT) or the particular type of macroblock. Such conventional approaches are discussed in (i) U.S. Pat. No. 5,774,593 entitled “Automatic scene decomposition and optimization of MPEG compressed video”, (ii) U.S. Pat. No. 5,493,345 entitled “Method for detecting a scene change and image editing apparatus”, and (iii) U.S. Pat. No. 5,642,174 entitled “Scene change detecting device”. Such conventional approaches do not detect scene changes before encoding the current frame, but rather provide post-recording scene change detection.
Other conventional approaches are based on the variation of statistics related to the video sequence. Different types of statistics are used, but such approaches base the detection of a scene change on the variation of that statistic from one frame to the other, usually by comparing the difference of statistics to a threshold.
Such approaches are discussed in U.S. Pat. No. 5,404,174, entitled “Scene change detector for detecting a scene change of a moving picture”. This method compares the frame activity from one frame to the other. Another approach is presented in U.S. Pat. No. 5,732,146, entitled “Scene change detecting method for video and movie”. This method compares the value of a histogram from one frame to the other. Another approach is discussed in U.S. Pat. No. 5,990,980, entitled “Detection of transitions in video sequences”. This method introduces a dissimilarity measure based on the difference of histograms between consecutive frames. Another approach is discussed in U.S. Pat. No. 5,617,149, entitled “Apparatus an method for detecting scene changes using the difference of MAD between image frames”. This method detects scene changes when the variation of the frame based DC value is bigger than a set threshold. Another approach is discussed in U.S. Pat. No. 5,589,884, entitled “Adaptive quantization controlled by scene change detection”. This method detects scene changes using a pixel based variation of DC between two consecutive frames. Another approach is discussed in U.S. Pat. No. 6,014,183, entitled “Method and apparatus for detecting scene changes in a digital video stream”. This methods compares pixel colors from one frame to the next frame to detect scene changes. Each of these approaches is based on a first order of derivation of the statistics used (i.e., DC, histogram, activity, etc.), and are fairly prone to invalid scene change detection.
Referring to FIG. 1, a diagram illustrating a conventional sequence of scene changes is shown. Clear discontinuities are shown as a transition 10 and a transition 12. The discontinuities between scenes (i.e., the transition 10 between a SCENE1 and a SCENE2 and the transition 12 between the SCENE2 and the SCENE3) are clear when monitoring the sequence.
Referring to FIG. 2, a diagram illustrating a conventional scene change and a fade out is shown. The discontinuities are shown at a transition 20 and a transition 22. The signal INPUT′ represents a first order derivative of the signal INPUT. The signal INPUT″ illustrates a second order derivative of the signal INPUT.
Referring to FIG. 3, a diagram illustrating a conventional scene change is shown. A first direction 30 illustrates a transition between a SCENE1 and a SCENE2. A second direction 32 illustrates a transition from the SCENE2 to the SCENE1. The transition has different characteristics in the direction 30 than in the direction 32. Conventional approaches only analyze the signal INPUT(T) in either the direction 30 from one direction than from the other direction.
Referring to FIG. 4, a diagram illustrating three conventional scene change cases is shown. Case 1 represents a scene change from a relatively fixed input value to a relatively fixed value. Case 2 illustrates a transition from a variable input value (i.e., scene 1) to a relatively fixed input value (i.e., scene 2). Case 3 illustrates a relatively fixed input value (i.e., scene 1) to a variable input value (i.e., scene 2).
It would be desirable to detect scene changes within a video sequence that (i) distinguishes between fades and discontinuities, (ii) selects a processing direction to minimize processing needs and/or (iii) processes while recording the video sequence.